The present invention relates to polyester resin compositions, and films, packaging materials, laminates and containers comprising the compositions. More specifically, the present invention relates to polyester resin compositions having excellent heatsealability, resistance to hydrogen peroxide, flavor-barrier properties, gas-barrier properties and mechanical properties such as elongation and strength, and also to films and the like comprising such compositions. The polyester resin compositions, films and the like of the present invention can, utilizing the above features, effectively be used for various uses, in particular as packaging materials for containers for beverages containing flavor ingredients.
The problem of the disposal of plastic containers having once been used has become a big social issue. Demand has therefore increased for paper containers, which can be incinerated or regenerated relatively simply and smoothly compared to plastic containers. This trend also holds for containers for beverages such as juices, and thus paper containers covered, on their inner surface, with resin films are generally used widely for containers for juices and the like. In this case, olefin resins are generally used as the resin films covering the inner surface of the paper containers. However, such paper containers covered on their inner surface with olefin resins will, when used for beverages containing flavor components, such as fruit juices, sometimes cause loss of flavor, change in taste and like problems.
Japanese Patent Application Laid-open No. 133638/1991 proposes, to solve the problems, covering the inner surface of paper containers with, instead of olefin resins, a polyester resin laminate comprising a layer of a modified polyethylene terephthalate containing about 5 to 20 mole % of a copolymerization component. This improvement is, due to the gas-barrier properties and flavor-barrier properties inherently possessed by polyester resin, successful in keeping good, to some extent, the level of the flavor and taste of the beverages or the like packed in the paper containers.
However, the covering layer comprising the above modified polyester resin laminate has several drawbacks as follows. That is, the covering layer tends, on sterilization by hydrogen peroxide, which treatment is widely adopted in the production process of paper containers, to swell, produce bubbles in the covering layer and partly delaminate from the paper base. These troubles markedly deteriorate the processability and process-runnability on the production of paper containers. Besides, the hydrogen, peroxide contained in the thus swollen covering layer comprising the polyester resin laminate migrates to the contents packed in the paper containers, which may lead to decreases in the quality and safety of the food contained.
Japanese Patent Application Laid-open No. 45883/1998 proposes use of a modified polyethylene terephthalate copolymerized with naphthalenedicarboxylic acid, in which the content of remaining metals has been suppressed to 10 millimoles % or below and the content of a phosphorus compound has been adjusted to 3 to 20 millimoles %, to improve the transparency and color tone of the copolyester. In this case, however, the features inherent in polyethylene terephthalate, such as resistance to hydrogen peroxide, are not sufficiently improved.
Under the above situation, the present inventors have studied to develop a polyester resin composition which can effectively be used for food containers and the like. That is, the present inventors have studied in order to provide a polyester resin composition which maintains at a good level the gas-barrier properties and flavor-barrier properties inherently possessed by polyester resins, does not cause, on sterilization with hydrogen peroxide, swelling, bubble generation, delamination from the base and like troubles, has excellent heatsealability, thereby being able to be bonded and laminated firmly and smoothly on bases such as paper, and is excellent in mechanical properties such as elongation in handleability.
As a result, the present inventors have found that a polyester resin composition having excellent gas-barrier and flavor-barrier properties, resistance to hydrogen peroxide, heatsealability and mechanical properties can be obtained by melt kneading under specific conditions a copolyester resin having specific contents of naphthalenedicarboxylic acid component and/or a specific diol component, which co-polyester resin has been mixed with an olefin polymer and a compatibility-improving agent in specific amounts. Japanese Patent Application Laid-open No. 302204/1997 was filed based on the above finding.
Based on the invention disclosed in the above Japanese Patent Application Laid-open No. 302204/1997, the present inventors have made a further study to achieve a better improvement technology.
As a result, the present inventors have found that the polyester resin composition of the invention of the above Japanese Patent Application Laid-open No. 302204/1997 is, when a specific amount of at least one metal compound selected from the group consisting of manganese compounds and cobalt compounds is incorporated therein, more improved in its resistance to hydrogen peroxide, while maintaining its excellent gas-barrier and flavor-barrier properties, heatsealability and mechanical properties. The resulting composition becomes markedly useful as molded articles such as film, packaging material for foods and like uses.
The present inventors have further found that another polyester resin composition having excellent resistance to hydrogen peroxide, as well as excellent gas-barrier and flavor-barrier properties, heatsealability and mechanical properties can be obtained by incorporation of both a manganese compound and a cobalt compound into the same copolyester resin containing a specific amount of naphthalenedicarboxylic acid as that used in the invention of the above Japanese Patent Application Laid-open No. 302204/1997.
The present inventors have still further found that, with the above two types of polyester resin compositions, incorporation of a specific amount of an alkali metal salt of an organic carboxylic acid and/or a phosphorus compound leads to further improvement of the resistance to hydrogen peroxide, thermal resistance and resistance to coloring, and completed the present invention based on these findings.
Thus, the present invention provides a polyester resin composition (hereinafter sometimes referred to as xe2x80x9cpolyester resin composition (A)xe2x80x9d)
(i) which comprises:
(a) units from a diol consisting essentially of ethylene glycol units and units from a dicarboxylic acid consisting essentially of terephthalic acid, as essential components, and units from naphthalenedicarboxylic acid in an amount of 5 to 40 mole % based on the total moles of all structural units;
(b) at least one metal compound selected from the group consisting of cobalt compounds and manganese compounds;
(c) an olefin polymer; and
(d) a compatibility-improving agent;
(ii) said metal compound being contained in an amount based on the weight-of said polyester resin of 100 to 1,000 ppm and said olefin polymer and compatibility-improving agent being contained in such amounts as to satisfy the following formulas {circle around (1)} and {circle around (2)}:
10 (parts by weight)xe2x89xa6X+Yxe2x89xa6100 (parts by weight)xe2x80x83xe2x80x83{circle around (1)}
1xe2x89xa6X/Yxe2x89xa690xe2x80x83xe2x80x83{circle around (2)}
xe2x80x83wherein X and Y represent, respectively, the content of the olefin polymer (parts by weight) based on 100 parts by weight of the polyester resin and that of the compatibility-improving agent on the same basis; and
(iii) which has been obtained by melt kneading in such a manner as to satisfy the following formula {circle around (3)}
E/Fxe2x89xa61xe2x80x83xe2x80x83{circle around (3)}
xe2x80x83where E=xcex71 (X+Y)/(xcex72X+xcex73Y)
F=100D2D3/D1(D3X+D2Y)
wherein X and Y are the same as defined for formulas {circle around (1)} and {circle around (2)}, xcex71, xcex72 and xcex73 represent, respectively, the melt viscosities (in poises) of the polyester resin, olefin polymer and compatibility-improving agent determined at the melt kneading temperature on preparation of the polyester resin composition, and D1, D2 and D3 represent, respectively, the densities at 25xc2x0 C. of the polyester resin, olefin polymer and compatibility-improving agent.
The present invention further provides a polyester resin composition (hereinafter sometimes referred to as xe2x80x9cpolyester resin composition (B)xe2x80x9d)
(i) which comprises:
(a) units from a diol consisting essentially of ethylene glycol and units from a dicarboxylic acid consisting essentially of terephthalic acid, as essential components, and units from naphthalenedicarboxylic acid in an amount of 5 to 40 mole % based on the total moles of all structural units;
(b) a cobalt compound; and
(c) a manganese compound
(ii) said cobalt compound and manganese compound being contained in such amounts as to satisfy the following formulas {circle around (5)} through {circle around (7)}:
0.01xe2x89xa6CCoxe2x89xa60.20xe2x80x83xe2x80x83{circle around (5)}
0.01xe2x89xa6CMnxe2x89xa60.20xe2x80x83xe2x80x83{circle around (6)}
0.02xe2x89xa6(CCo+CMn)xe2x89xa60.30xe2x80x83xe2x80x83{circle around (7)}
wherein CCo and CMn represent, respectively, the mole % based on the total moles of all dicarboxylic acid units present in the polyester resin of the cobalt compound in terms of cobalt atom and that of manganese compound in terms of manganese atom.
The present invention also includes a polyester resin composition comprising the above polyester resin composition (A) or (B) and further comprising an alkali metal salt of an aliphatic carboxylic acid having 1 to 15 carbon atoms in an amount of 100 to 10,000 ppm in terms of the alkali metal atom based on the weight of the polyester resin contained in said composition.
The present invention further includes a polyester resin composition comprising the above polyester resin composition (A) and further comprising a phosphorus compound in such an amount as to satisfy the following formula {circle around (4)}
(CP/CM)xe2x89xa60.65xe2x80x83xe2x80x83{circle around (4)}
wherein CP and CM represent, respectively, the mole % based on the total moles of dicarboxylic acid units contained in the polyester resin of the phosphorus compound in terms of phosphorus atom and that of the metal compound in terms of the metal atom.
The present invention still further includes a polyester resin composition comprising the above polyester resin composition (B) and further comprising a phosphorus compound in such an amount as to satisfy the following formula {circle around (4)}
CP/(CCo+CMn)xe2x89xa60.65xe2x80x83xe2x80x83{circle around (4)}
wherein CP, CCo and CMn represent, respectively, the mole % based on the total moles of dicarboxylic acid units contained in the polyester resin of the phosphorus compound in terms of phosphorus atom, that of the cobalt compound in terms of cobalt atom and that of the manganese compound in terms of manganese atom.
The present invention yet further includes molded articles such as film and packaging materials comprising the above polyester resin compositions, laminates comprising a layer of the above polyester resin compositions and a paper layer, and paper containers covered on the inner surface thereof with the polyester resin compositions.
The polyester resin constituting the main component of the polyester resin compositions of the present invention consists essentially of units from a diol consisting essentially of ethylene glycol and units from a dicarboxylic acid consisting essentially of terephthalic acid and further comprises units from naphthalenedicarboxylic acid.
With the polyester resin used in the present invention, it is desirable, in order to provide the resulting polyester resin compositions with good gas-barrier properties and flavor-barrier properties, that the content based on the total moles of all structural units constituting the polyester resin of terephthalic acid units be 10 to 45 mole %, more preferably 15 to 42.5 mole %, and that the content of ethylene glycol units be 10 to 50 mole %, more preferably 20 to 50 mole % on the same basis.
With the polyester resin used in the present invention, it is necessary that naphthalenedicarboxylic acid units be contained in an amount, based on the total moles of all structural units constituting the polyester resin, of 5 to 40 mole %, more preferably 7.5 to 35 mole %. If the content of naphthalenedicarboxylic acid units in the polyester resin is less than 5 mole %, the resulting polyester resin compositions will have poor heatsealability and will, on sterilization with hydrogen peroxide, swell to a large extent. On the other hand, if the content of naphthalene-dicarboxylic acid units in the polyester resin exceeds 40 mole %, the resulting polyester resin composition will also have poor heatsealability.
The polyester resin used in the present invention may possess structural units other than those mentioned above, within limits not to impair the heatsealability, gas-barrier and flavor-barrier properties and like features. Examples of such other structural units are diol units derived from diols, e.g. diethylene glycol, butanediol, polyethylene glycols (preferably those having a molecular weight of 400 to 30,000) and 1,4-cyclohexanedimethanol; and dicarboxylic acid units derived from aromatic dicarboxylic acids, e.g. isophthalic acid and sodium sulfoisophthalate, aliphatic dicarboxylic acids, e.g. succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid and sebacic acid; and ester-forming derivatives of the foregoing. The polyester resin may contain one or at least two kinds of the above other structural units. In general, it is desirable that the content of the other structural units be not more than about 5 mole % based on the total moles of all structural units constituting the polyester resin.
It is also desirable in view of film formability and film strength, that the polyester resin used in the present invention have an intrinsic viscosity (determined in a 1/1 by weight mixed solvent of phenol/tetrachloroethane at 30xc2x0 C.) of 0.60 to 1.50 dl/g.
The polyester resin composition (A) of the present invention contains at least one metal compound selected from the group consisting of cobalt compounds and manganese compounds. The polyester resin composition (A) may either contain a cobalt compound only or a manganese compound only; or, it may contain both a cobalt compound and a manganese compound.
On the other hand, it is necessary that the polyester resin composition (B) contain both of a cobalt compound and a manganese compound.
Examples of cobalt compounds usable for the polyester resin composition (A) and polyester resin composition (B) of the present invention (hereinafter these compositions are sometimes referred inclusively as xe2x80x9cpolyester resin compositionsxe2x80x9d) are cobalt salts of aliphatic acids, e.g. cobalt formate, cobalt acetate and cobalt propionate; cobalt halides, e.g. cobalt chloride, cobalt bromide; cobalt iodide and cobalt fluoride; cobalt sulfate; cobalt sulfide, cobalt oxide and cobalt hydroxide.
Examples of manganese compounds usable for the polyester resin compositions of the present invention are manganese salts of aliphatic acids, e.g. manganese formate, manganese acetate and manganese propionate; manganese halides, e.g. manganese chloride, manganese bromide, manganese iodide and manganese fluoride; manganese sulfate; manganese sulfide; manganese oxide and manganese hydroxide.
The polyester resin composition (A) of the present invention can contain one or at least two kinds of the above cobalt compounds and manganese compounds.
The polyester resin composition (B) of the present invention can contain a combination of one or at least two kinds of the above cobalt compounds and one or at least two kinds of the above manganese compounds.
Among the above compounds, for the polyester resin compositions of the present invention, cobalt acetate and/or cobalt sulfate are preferably used as cobalt compound and manganese acetate and/or manganese sulfate are preferably used as manganese compound.
The polyester resin composition (A) contains at least one metal compound selected from the group consisting of cobalt compounds and manganese compounds, in an amount of 100 to 1000 ppm in terms of metal atom based on the weight of the polyester resin present in the polyester resin composition (A) (i.e. 0.01 to 0.1 part by weight in terms of metal atom based on 100 parts by weight of the polyester resin).
If the content of the above metal compound (cobalt compound and/or manganese compound) in the polyester resin composition (A) is less than the above-described 100 ppm, the composition will swell to a large extent on sterilization with hydrogen peroxide. On the other hand, if the content of the above metal compound (cobalt compound and/or manganese compound) in the polyester resin composition (A) exceeds the above-described 1000 ppm, the polyester resin will decompose on melt molding of the polyester resin composition (A), so that the strength of the obtained molded articles such as film will decrease. In view of more effective suppression of swelling on sterilization with hydrogen peroxide and of decomposition of the polyester resin on melt molding, the content of the metal compound is preferably 150 to 800 ppm in terms of metal atom based on the weight of the polyester resin.
It is necessary that the polyester resin composition (B) contain both a cobalt compound and a manganese compound in such amounts as to satisfy the following formulas {circle around (5)} through {circle around (7)}:
0.01xe2x89xa6CCoxe2x89xa60.20xe2x80x83xe2x80x83{circle around (5)}
0.01xe2x89xa6CMnxe2x89xa60.20xe2x80x83xe2x80x83{circle around (6)}
0.02xe2x89xa6(CCo+CMn)xe2x89xa60.30xe2x80x83xe2x80x83{circle around (7)}
wherein CCo and CMn represent, respectively, the mole % based on the total moles of all dicarboxylic acid units present in the polyester resin of the cobalt compound in terms of cobalt atom and that of manganese compound in terms of manganese atom.
If, in the polyester resin composition (B), the content, based on the total moles of all dicarboxylic acid units of the polyester resin, of the cobalt compound is less than 0.01 mole % in terms of cobalt atom, that of the manganese compound is less than 0.01 mole % in terms of manganese atom, or that of the cobalt compound and manganese compound in terms of the sum of cobalt atom and manganese atom is less than 0.02 mole %, the composition will swell to a large extent on sterilization with hydrogen peroxide. On the other hand, if the content, based on the total moles of all dicarboxylic acid units of the polyester resin, of the cobalt compound in the polyester resin composition (B) exceeds 0.20 mole % in terms of cobalt atom, that of the manganese compound exceeds 0.20 mole % in terms of manganese atom, or that of the cobalt compound and manganese compound exceeds 0.30 mole % in terms of the sum of cobalt atom and manganese atom, the polyester resin will decompose on melt molding of the polyester resin composition (B), so that the strength of the obtained molded articles such as film will decrease.
With the polyester resin composition (B), in view of better resistance of the composition to hydrogen peroxide and that of the polyester resin to thermal decomposition, the above content (CCo) of the cobalt compound is preferably in a range of 0.02 to 0.15 mole %, that (CMn) of the manganese compound is preferably in a range of 0.02 to 0.15 mole % and the total content (CCo+CMn) of the cobalt compound and manganese compound is preferably in a range of 0.04 to 0.20 mole %.
With the polyester resin composition (B), incorporation of a cobalt compound and a manganese compound in amounts satisfying the above formulas {circle around (5)} through {circle around (7)} into the above polyester resin containing naphthalenedicarboxylic units in the above specific amount insures excellent heatsealability, resistance to hydrogen peroxide, flavor-barrier properties, gas-barrier properties and mechanical properties such as elongation and strength.
The polyester resin composition (A) of the present invention comprises, in addition to the above cobalt compound and/or manganese compound, a third component of an olefin polymer. Ethylene polymers are preferably used as the olefin polymer, in view of heatsealability, suppression of swelling on sterilization with hydrogen peroxide and the strength and elongation of the resultant films. Examples of ethylene polymers preferably usable are high density polyethylene, low density polyethylene, linear low density polyethylene and ethylene-vinyl acetate copolymer. Among these, high density polyethylene, which can suppress film breakage on film formation, is more preferably used. It is preferred, although not necessarily limited thereto, that the olefin polymer used for the polyester resin composition (A) have a melt flow rate (MFR) of about 1 to 3 g/10 minutes, in view of suppression of neck-in trouble on film formation.
The polyester resin composition (A) of the present invention comprises a fourth component of a compatibility-improving agent. The compatibility-improving agent is, for the polyester resin composition (A), used in order to disperse finely a dispersed phase comprising the olefin polymer used, in the polyester resin forming a matrix phase and, at the same time, to increase the interfacial adhesiveness between the polyester resin phase and the olefin polymer phase.
Preferably usable as the compatibility-improving agent are polymers possessing in the molecule thereof both a structural part having affinity to the polyester resin and another structural part having affinity to the olefin polymer used. Preferred examples of such polymers are block copolymers and graft copolymers possessing a polymeric part having affinity to the polyester resin and another polymeric part having affinity to the olefin polymer; and polymers having affinity to the olefin polymer and containing in the molecule thereof groups reactable with the terminal hydroxyl group and/or terminal carboxyl group of the polyester resin.
Examples of particularly preferred compatibility-improving agents among the above are the following polymers: (1) ethylene/(meth)acrylic acid copolymers, (2) ethylene/(meth)acrylic acid copolymers crosslinked with metal ion (ionomers), (3) block copolymers comprising blocks of styrene/ethylene/butadiene copolymer having carboxyl groups or derivatives thereof and blocks of styrene polymer, and (4) block copolymers comprising blocks of an olefin polymer having carboxyl groups or derivatives thereof and blocks of styrene polymer. The polyester resin composition (A) of the present invention may contain only one or at least two kinds of these polymer-based compatibility-improving agents.
Ethylene/acrylic acid copolymer is preferred of the (1) ethylene/(meth) acrylic acid copolymers mentioned above as compatibility-improving agent. With this copolymer, the copolymerization ratio of acrylic acid is more preferably 4 to 15% by weight, which leads to better mechanical properties of the resulting polyester resin composition (A) and films and the like obtained therefrom. If the copolymerization ratio of acrylic acid is less than 4% by weight, sufficient affinity to the polyester resin phase will not be exhibited and the resulting polyester resin composition (A) and films and the like formed therefrom will tend to have poor mechanical properties. On the other hand, if the copolymerization ratio of acrylic acid in the ethylene/acrylic acid copolymer exceeds 15% by weight, gels will sometimes be generated in the resulting polyester resin composition (A).
Ethylene/methacrylic acid copolymer crosslinked with metal ion is preferably used of the (2) ethylene/(meth)-acrylic acid copolymer crosslinked with metal ion (ionomers) mentioned above as the compatibility-improving agent. With this ionomer, the copolymerization ratio of methacrylic acid is preferably 5 to 15% by weight, in view of the mechanical properties of the resulting polyester resin composition (A) and films and the like obtained therefrom and of suppression of gel generation.
The block copolymers (3) and (4) having carboxyl group or derivatives thereof mentioned above as the compatibility-improving agent comprise block copolymers comprising styrene/ethylene/butadiene copolymer blocks and styrene polymer blocks or block copolymers comprising olefin polymer blocks and styrene polymer blocks, both modified with a carboxylic acid such as maleic anhydride, maleic acid, fumaric acid, itaconic acid, acrylic acid, crotonic acid or maleic imide, or derivatives thereof. Among these, the above block copolymers modified with maleic anhydride are preferably used. In this case, the amount of modification with maleic anhydride in the block copolymers is preferably 0.5 to 3% by weight based on the total weight of the block copolymers, in view of the mechanical properties and suppression of gel generation of the resulting polyester resin compositions (A) and films obtained therefrom.
The polymer-based compatibility-improving agent used for the polyester resin composition (A) desirably has a melt flow rate (MFR) of about 1 to 7 g/10 min, in view of film strength.
The polyester resin composition (A) of the present invention comprises the above polyester resin, olefin polymer and compatibility-improving agent in such amounts as to satisfy the following formulas {circle around (1)} and {circle around (2)}:
10 (parts by weight)xe2x89xa6X+Yxe2x89xa6100 (parts by weight)xe2x80x83xe2x80x83{circle around (1)}
1xe2x89xa6X/Yxe2x89xa690xe2x80x83xe2x80x83{circle around (2)}
wherein X and Y represent, respectively, the content of the olefin polymer (parts by weight) based on 100 parts by weight of the polyester resin and that of the compatibility-improving agent on the same basis.
If, in the polyester resin composition (A) , the total content (X+Y) of the olefin polymer and compatibility-improving agent is less than 10 parts by weight based on 100 parts by weight of the polyester resin, thus deviating from the above formula {circle around (1)}, the resulting polyester resin composition (A) and films and the like comprising the same will, when exposed to hydrogen peroxide, absorb the hydrogen peroxide, which leads to swelling, bubble generation, delamination from the base such as paper and like troubles. On the other hand, if the total content (X+Y) of the olefin polymer and compatibility-improving agent in the polyester resin composition (A) exceeds 100 parts by weight based on 100 parts by weight of the polyester resin, thus also deviating from the above formula {circle around (1)}, the gas-barrier properties and flavor-barrier properties of the resulting polyester resin composition (A) and films and the like comprising the same will be impaired. With the polyester resin composition (A) of the present invention, the total content of the olefin polymer and compatibility-improving agent is preferably 20 to 70 parts by weight based on 100 parts by weight of the polyester resin, which insures better resistance to, hydrogen peroxide, thereby being capable of effectively preventing swelling, bubble generation and delamination from the base, and better gas-barrier properties and flavor-barrier properties.
If the ratio (X/Y) between the content of the olefin polymer in the polyester resin composition (A) and that of the compatibility-improving agent is less than 1, thus deviating from the above formula {circle around (2)}, the content of the compatibility-improving agent in the polyester resin composition (A) will become too high, so that gels will be generated. On the other hand, if the ratio (X/Y) between the content of the olefin polymer in the polyester resin composition (A) and that of the compatibility-improving agent exceeds 90, thus deviating from the above formula {circle around (2)}the content of the compatibility-improving agent in the polyester resin composition (A) will become too low to achieve good compatibility between the polyester resin phase and the olefin polymer phase, so that the physical properties for example mechanical properties such as strength and elongation of the resulting polyester resin composition (A) and films and the like obtained therefrom are impaired. The above ratio (X/Y) in the polyester resin composition (A) of the present invention is preferably in a range of 1 to 40.
It is necessary that the polyester resin composition (A) of the present invention have, besides satisfying the above requirements, been obtained by melt kneading in such a manner as to satisfy the following formula {circle around (3)}
E/Fxe2x89xa61xe2x80x83xe2x80x83{circle around (3)}
where E=xcex71(X+Y)/(xcex72X+xcex73Y)
F=100D2D3/D1(D3X+D2Y)
wherein X and Y are the same as defined for formulas {circle around (1)} and {circle around (2)}, xcex71, xcex72 and xcex73 represent, respectively, the melt viscosities (in poises) of the polyester resin, olefin polymer and compatibility-improving agent determined at the melt kneading temperature on preparation of the polyester resin composition, and D1, D2 and D3 represent, respectively, the densities at 25xc2x0 C. of the polyester resin, olefin polymer and compatibility-improving agent.
To this end, it becomes necessary to make appropriate the amounts to be mixed of the polyester resin, olefin polymer and compatibility-improving agent to be used, the selection of the above three components having appropriate densities, the selection of the above three components capable of exhibiting the viscosities at the melt kneading temperature actually adopted satisfying the formula {circle around (3)}, and the selection of melt kneading temperature and like conditions for preparing the polyester resin composition (A). Taking the above points into consideration, by selecting appropriate polymers and employing suitable melt kneading conditions, one can obtain the polyester resin composition (A) of the present invention that satisfies the above formula {circle around (3)}.
Polyester resin compositions and films and the like obtained therefrom, with the value of E/F exceeding 1 and not satisfying formula {circle around (3)}, have poor flavor-barrier properties even if such polyester resin compositions have been prepared by melt kneading. The reason for this is, being not clear though, estimated to be as follows. That is, with the value of E/F exceeding 1, the polyester resin does not form a matrix in the obtained polyester resin composition, while the olefin polymer and/or compatibility-improving agent does, so that the good gas-barrier properties inherently possessed by the polyester resin cannot be exhibited.
Although a smaller value of the above ratio E/F results in easier matrix formation of the polyester resin in the polyester resin composition, too small a value of E/F tends to cause problems such as decrease in resistance to hydrogen peroxide. With the polyester resin composition (A) , the value of E/F is preferably 0.1 to 0.9.
The polyester resin composition (A) of the present invention, which comprises, together with a cobalt compound and/or a manganese compound, an olefin polymer and a compatibility-improving agent in such amounts as to satisfy the above formulas {circle around (1)} and {circle around (2)}, and also satisfy the above formula {circle around (3)} is excellent in heatsealability, resistance to hydrogen peroxide, flavor-barrier properties, gas-barrier properties and mechanical properties such as elongation and strength, as well as in flexibility and folding processability.
The polyester resin composition (A) and polyester resin composition (B) of the present invention can comprise in addition to the above-described components, an alkali metal salt of an aliphatic carboxylic acid having 1 to 15 carbon atoms. Then, the compositions are provided with still better resistance to hydrogen peroxide and can more effectively suppress swelling on sterilization with hydrogen peroxide. Examples of usable alkali metal salts of aliphatic carboxylic acids having 1 to 15 carbon atoms are sodium formate, sodium acetate, potassium acetate, sodium propionate, potassium propionate, sodium butyrate, potassium butyrate, sodium valerate, potassium valerate, sodium caproate, potassium caproate, sodium caprate, potassium caprate, sodium laurate, potassium laurate, sodium myristate and potassium myristate. The salts may be used either singly or in combination of two or more.
The content of the above alkali salt of an aliphatic carboxylic acid in the polyester resin composition (A) and/or polyester resin composition (B) is preferably 100 to 10,000 ppm in terms of the alkali metal atom based on the weight of the polyester resin present in the polyester resin composition (0.01 to 1 part by weight based on 100 parts by weight of the polyester resin) , more preferably 1,500 to 8,000 ppm on the same basis.
The polyester resin used for the polyester resin compositions of the present invention can be produced, with no specific restrictions, by any process generally adopted for general-purpose polyester resins such as polyethylene terephthalate. For example, one can use a polyester resin-forming material comprising a dicarboxylic acid component comprising a dicarboxylic acid consisting essentially of terephthalic acid or lower alkyl esters thereof and a diol component consisting essentially of ethylene glycol, which material further comprises naphthalenedicarboxylic acid or ester-forming derivatives thereof in such an amount as to permit the copolymerization ratio of naphthalenedicarboxylic acid units in the resulting polyester to fall into the above range of 5 to 40 mole %. This material is subjected to esterification or transesterification to form a low-molecular-weight polymer, which is then melt polycondensed into a polyester. The obtained polyester is formed into chips, pellets or the like having any optional shape, which are as desired further subjected to solid-phase polymerization to yield the desired polyester resin.
A preferable process, though not limited thereto, for producing the polyester resin is now more concretely described. It is recommended, on producing the above low-molecular-weight polymer by esterification, to subject the above polyester resin-forming material to esterification at a temperature of about 230 to 280xc2x0 C. under atmospheric pressure or under an absolute pressure of not higher than 3 kg/cm2. On this occasion, it is desirable to use the dicarboxylic acid component and the diol component in a molar ratio of 1:1 to 1:1.5.
Where transesterification is employed to produce the low-molecular-weight polymer, it is recommended to subject the above polyester resin-forming material at about 170 to 230xc2x0 C. under atmospheric pressure or under a pressure close to atmospheric pressure. On this occasion, it is desirable to use the dicarboxylic acid component and the diol component in a molar ratio of 1:1 to 1:3. Examples of catalysts usable for the transesterification are metal compounds similar to the manganese compound or cobalt compound contained in the polyester resin compositions of the present invention, and titanic acid esters, which have been widely used, such as tetraisopropyl titanate, tetrabutyl titanate and tetrastearyl titanate.
The above melt polycondensation for producing the polyester resin from a low-molecular-weight polymer can be carried out, generally, in the presence of a polycondensation catalyst such as germanium dioxide or antimony trioxide, at a temperature of about 260 to 290xc2x0 C. In conducting this polycondensation, it is desirable to use germamium dioxide in an amount of 50 to 300 ppm, which can suppress swelling on treatment with hydrogen peroxide.
The melt polycondensation yields, generally, a, polyester having an intrinsic viscosity of 0.50 to 1.50 dl/g.
It is also desirable to conduct the above melt polycondensation with addition of a phosphorus compound, e.g. phosphoric acid, phosphorous acid, trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate and triphenyl phosphate, which can prevent the resulting polyester from coloring by thermal decomposition and from decrease in molecular weight on melt molding.
Too much content of a phosphorus compound in the polyester resin and in the polyester resin composition will, however, decrease the resistance to hydrogen peroxide of the polyester resin composition, since the phosphorus compound deactivates the cobalt compound or manganese compound used.
It is therefore recommended, with the polyester resin composition (A), to adjust the amount of the phosphorous compound to be added on melt polycondensation such that its content in the composition satisfies the following formula {circle around (4)}
(CP/CM)xe2x89xa60.65xe2x80x83xe2x80x83{circle around (4)}
wherein CP and CM represent, respectively, the mole % based on the total moles of dicarboxylic acid units contained in the polyester resin of the phosphorus compound in terms of phosphorus atom and that of the metal compound (cobalt compound and/or manganese compound) in terms of the metal atom.
With the polyester resin composition (B), it is recommended to adjust the amount of the phosphorous compound to be added on melt polycondensation such that its content in the composition satisfies the following formula {circle around (4)}
CP/(CCo+CMn)xe2x89xa60.65xe2x80x83xe2x80x83{circle around (4)}
wherein CP, CCo and CMn represent, respectively, the mole % based on the total moles of dicarboxylic acid units contained in the polyester resin of the phosphorus compound in terms of phosphorus atom, that of the cobalt compound in terms of cobalt atom and that of the manganese compound in terms of manganese atom.
The above esterification, transesterification and polycondensation may as necessary be conducted with addition of a diethylene glycol byproduction-suppressing agent, such as tetraammonium hydroxide, triethanolamine or triethylamine.
The polyester obtained by the above melt polycondensation is generally formed into chips or pellets, which are, as desired, preliminarily crystallized at a temperature of 190xc2x0 C. or below and can then be subjected to solid phase polymerization. The solid phase polymerization is, desirably, conducted by heating the chips (pellets) at about 190 to 240xc2x0 C. under reduced pressure or in stream of an inert gas such as nitrogen, while chips (pellets) are fluidized to prevent sticking by fusion. In view of the mechanical properties and viscosity on melt molding of the resulting polyester resin, it is recommended to continue the solid phase polymerization up to a stage where the finally obtained polyester resin has an intrinsic viscosity (determined at 30xc2x0 C. in a 1/1 by weight mixed solvent of phenol/tetrachloroethane) in a range of about 0.60 to 1.50 dl/g.
By carrying out the above series of processes, the polyester which is preferably used for the polyester resin compositions of the present invention is obtained.
The polyester resin compositions of the present invention may, within limits not to impair the purpose of the invention, incorporate various known additives, e.g. hydrolysis-preventing agent, color, flame retardant, antioxidant, UV absorber, antistatic agent and lubricant. Where, however, the polyester resin compositions of the present invention are used at places directly touching foods, as is the case with covering material for the inner surface of paper containers for foods, it becomes necessary to take safety problems sufficiently into consideration on selecting the type of the additives used.
In producing the polyester resin composition (A) of the present invention, it is necessary to melt knead the above components under such conditions as to satisfy the above formula {circle around (3 )}, in order to permit the polyester resin phase to form, in the resultant polyester resin composition, a matrix, in which the olefin polymer phase is dispersed uniformly and finely by the compatibility-improving action exhibited by the compatibility-improving agent used.
For the melt kneading, one may select a process which comprises at first producing the polyester resin in a polymerization vessel and then, after addition of an olefin polymer and a compatibility-improving agent into the vessel, conducting melt kneading. It is however recommended, in view of productivity and homogeneous mixing, to use an extruder or like melt kneaders. When such a melt kneader is used, the melt kneading temperature is preferably about 220 to 300xc2x0 C., more preferably 240 to 280xc2x0 C., which insures production of the polyester resin compositions having good physical properties. If the melt kneading temperature employed on production of the polyester resin composition (A) is lower than 220xc2x0 C., the functional groups present in the compatibility-improving agent will not sufficiently react with the terminal hydroxyl groups or carboxyl groups of the polyester resin, so that it becomes difficult to provide the resulting polyester resin composition or films and the like obtained therefrom with good physical properties. On the other hand, if the temperature exceeds 300xc2x0 C., the polymer will undergo thermal decomposition markedly, thereby yielding a polyester resin composition as well as films obtained therefrom which tends to have poor physical properties.
With the polyester resin composition (A), there are no specific restrictions with respect to the processes for adding at least one metal compound selected from the group consisting of cobalt compounds and manganese compounds and for adding the above alkali metal salt of an organic carboxylic acid and phosphorus compound which may be used as occasions demand. The addition may thus be done at any time before, during or after melt kneading of the polyester resin, olefin polymer and compatibility-improving agent. Also, on transesterification or esterification to produce the polyester resin, a cobalt compound and/or manganese compound, as well as, as occasions demand, an alkali metal salt of an organic carboxylic acid and/or a phosphorous compound may be added as catalyst components or additives in specific amount to the reaction mixture, to produce the polyester resin composition (A) containing the cobalt compound and/or manganese compound and, as occasions demand, the alkali metal salt and/or the phosphorous compound.
With the polyester resin composition (B) , there are no specific restrictions with respect to the process for adding a cobalt compound and manganese compound, either. Thus, the cobalt compound and manganese compound, as well as the above alkali metal salt of an organic carboxylic acid and phosphorus compound which may be used as occasions demand, can be added during or after the production of the polyester resin, to produce the polyester resin composition (B).
The polyester resin compositions of the present invention may have any shape with no specific limitation, but it is desirable to shape them into pellets or chips, which are conveniently usable for various molding processes.
The polyester resin compositions of the present invention can be heat-melt molded into various shaped articles, e.g. films, sheets, plates, pipes, hollow products, die-shaped articles and laminates. To shape these items, any process usable for molding thermoplastic resins in general can be used. Examples of the process are extrusion, casting, extrusion blow molding, injection molding, injection blow molding, calendering, pressing, thermoforming and various lamination molding.
The polyester resin compositions of the present invention are effectively usable when, in particular, shaped into packaging films and sheets, bottles and like shaped packaging containers, which products utilize the excellent features of the composition, including gas-barrier properties, flavor-barrier properties, heatsealability, resistance to hydrogen peroxide and mechanical properties. Especially, the compositions are suitable as films, sheets, containers and similar packaging materials for foods. Where the polyester resin compositions of the present invention are shaped into films or sheets, the thickness of these items may be appropriately set, with no specific limitation, depending on use. It is however generally recommended to make them about 0.005 to 1 mm thick.
For producing films or sheets from the polyester resin compositions of the present invention, any known process for producing films or sheets from thermoplastic resins can be used. Examples of usable processes are extrusion through T-die; tubular film extrusion which comprises extruding through a circular die, while introducing a fluid into the extruded hollow cylinder; casting; calendering and pressing. Of these processes, in order to produce films in large-scale commercial production, it is preferred to use extrusion, in particular tubular film extrusion, which insures ready molding, Less waste and low production cost. On production of films by tubular film extrusion, oriented films can, as necessary, be obtained at the same time with the extrusion, by adjusting the pressure and flow rate of the fluid introduced into the hollow cylindrical article extruded through the circular die, and the take-up speed of the extruded film.
The films or sheets comprising the polyester resin compositions of the present invention may be formed into 2-layer or at least 3-layer laminates with other base materials. Examples of the other base materials to be used on this occasion are thermoplastic polymers, e.g. polyolefins such as polyethylene and polypropylene, polyamides, polyvinyl chloride, polyvinylidene chloride, polyesters other than the above and ethylene-vinyl alcohol copolymer; paper; fabrics; and metal foils. These base materials may be used singly or in combination of 2 or more. These laminates may be produced by any known process with no particular limitation, such as extrusion lamination, dry lamination, wet lamination or hot-melt lamination.
In particular, laminates comprising paper and, laminated thereon, a film comprising any one of the polyester resin compositions of the present invention can effectively be used as materials for paper containers for fruit juices and similar beverages. Paper containers having on the inner surface thereof a film layer comprising any one of the polyester resin composition of the present invention have the following features. On sterilization with hydrogen peroxide, these containers do not swell, generate bubbles in the polyester resin composition layer or cause delamination between the polyester resin layer and the paper base. Moreover, these containers can maintain safely and at good levels the flavor and taste of the beverage packed therein, over a long period of time.